newsupernova/vendor/magento/module-backend/view/adminhtml/templates/admin/login_buttons.phtml

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
?>
<div class="actions">
    <button
        <?php $block->getUiId(); ?>
        class="action-login action-primary">
        <span><?= /* @escapeNotVerified */ __('Sign in') ?></span>
    </button>
</div>